The engine on a vehicle drives an alternator which generates an unregulated alternating current (AC) which is rectified to provide a direct current (DC) power source which is used to recharge the battery which is necessary to start the engine and also maintain the electrical systems which are used on the vehicle.
The alternating current (AC) of the alternator is passed through a rectifying circuit, normally a bridge rectifier or a half bridge rectifier in order to produce a DC power source. With constant excitation the alternator will produce an AC voltage which is proportional to the speed of the engine. Further, the AC voltage will have a frequency which is directly dependent upon the speed of the engine. In this unregulated form, i.e. without a fixed frequency, the output of the alternator is unsuitable for powering AC devices which are normally available for household use. In particular, such AC source is unsuitable to power sensitive instruments or devices such as computers or other electronic devices which require a constant frequency and voltage, normally 60 Hz at 120 Volts AC.
In remote areas or construction sites, the only available source of power may be a vehicle. Therefore, it would be desirable if the vehicle engine could be used as a source to operate power hand tools or operate electronic equipment.
To produce a regulated AC supply from existing technology, devices generally comprise a first stage which produces a DC voltage in excess of a desired AC peak voltage. The second stage of the standard technology involves an inverter circuit fed by the DC voltage source. Since the output requires a smooth sine wave generation, a high frequency converter mode is required. Transistor switching has been found to be the only acceptable method for such high frequency switching. However, it has been found that since the desired output AC voltage is 120 volts AC, the stress on such switching components for such components to operate is at the upper limit. The result is that the switching transistors produce a considerable voltage drop at higher voltages and accordingly become very inefficient.
Further, the existing technology generally utilises transistor switching devices in series with the load increasing the voltage drop and thereby resulting in poor control capability of the load.